Temperature is a major driver of microbial plankton metabolism and ecosystem function although its interactions with other variables such as nutrient availability or predation pressure have precluded a comprehensive assessment of its role in the coastal ocean. Ecological theories linking temperature to metabolism, body size and abundance have been successfully applied to many groups of organisms including phytoplankton, with heterotrophic bacteria being frequently left aside. For instance, the growing consensus that bacterial biomass will increase in a warmer ocean likely characterized by lower phytoplankton biomass contradicts the predictions of the metabolic theory of ecology. Unraveling the reasons for this apparent departure underlies the objectives of this project. Both the biodiversity and functioning of pelagic ecosystems will likely be affected by temperature changes.

COMITE will address the effects of future warming on the ecology and biogeochemical role of temperate coastal microbial assemblages through three different approaches:

1. a retrospective analysis of the linkages between temperature, other environmental drivers and bacterial community structure and size-abundance relationships in a coastal time-series initiated in 2002 off Xixón, Spain (southern Bay of Biscay);

2. monthly experiments assessing the response of different bacterial groups to ambient temperature plus -3 and +3ºC over a complete annual cycle;

The final goal of COMITE data analysis is to build a predictive, testable model on the effects of realistic temperature rises on the biogeochemical role of oceanic bacteria. Among other novel approaches, the project will:

1. test for the first time whether enhanced metabolism due to higher temperature will result in lower bacterial biomass;

2. integrate bacterial phylogenetic and physiological structure within the temperature response as formulated in the metabolic theory of ecology.